We have been studying the pokeweed mitogen (PWM)-induced differentiation of human peripheral blood B lymphocytes. In this culture system, T cells are required. Furthermore, PWM activates functionally-distinct subsets of T cells, including helper, suppressor and inducer for T-T-cell interactions. Although these activated subsets carry the shared marker detected by the monoclonal antibody OKT4, reagents for distinguishing these functionally heterogeneous T-cell subsets are not available. Since it is difficult to define and characterize the functions of these T-cell subsets without separation, we propose to analyze T-cell subsets through the use of selective cloning techniques. We will (1) clone proliferating T cells using a limiting dilution or micromanipulation method; (2) functionally characterize cloned T cells in terms of their reactivity to PWM and autologous HLA-DR antigen, their ability to help or suppress B-cell differentiation and their ability to affect the effector function of other T-cell subsets by T-T cell interactions; (3) develop monoclonal antibodies directed against T-cell subsets with distinct immunological functions: (4) analyze functions of peripheral blood T-cell subsets using monoclonal antibodies in PWM-induced polyclonal and antigen-induced antibody responses. The result of this investigation will provide detailed insight into the regulatory interactions between T and B cells that ultimately drive B cells into Ig-secreting cells. In the future, monoclonal antibodies which distinguish T-cell subsets will be invaluable reagents to investigate T-cell anomalies in various forms of immunodeficiency diseases and malignancies of lymphoid cell origin.